This application is based on the application No. 2000-287375 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing a preform for compounding use, which is used, for example, in a casting process for making a brake disk rotor.
2. Description of the Prior Art
When a brake disk, which is one of parts constituting an automobile, is produced using an aluminum alloy by means of a casting process, the heat resistivity or wear resistance (i.e. anti-wear performance) of a sliding surface of the brake disk is reinforced by the following process. That is, at first, a preform such as a porous ceramic body or the like is disposed in a casting die. Then the preform is impregnated with a molten metal to be compounded with a matrix material.
As a conventional example of the above-mentioned type of preform, Japanese Laid-open Patent Publication No. 7-108370 discloses a preform, which is produced by means of the following process. That is, at first, titania (TiO2) and alumina (Al2O3) in the form of inorganic fibers are mixed with a solvent Then the mixture, in which titania and alumina are non-uniformly dispersed, is dried up and formed into a predetermined shape to obtain the preform.
Meanwhile, Japanese Laid-open Patent Publication No. 6-182524 discloses another preform, which is produced by means of the following process using aluminum borate whiskers (9Al2O3.2B2O3). That is, at first, sodium silicate and silicon carbide are added to the aluminum borate whiskers. Then the mixture is compacted to obtain the preform.
In addition, Japanese Laid-open Patent Publication No. 6-322459 (corresponding to European Patent Specification EP 0 624 657 B1) discloses a further preform, which is formed by mixing short fibers composed of alumina and silica with non-spherical mullite particles composed of alumina and silica.
Upon this, for example, the preform is formed by means of the following process. That is, SiC, TiO2 and CaCO3 of particle states, and aluminum borate whiskers and alumina short fibers for forming a skeleton of the preform are mixed with a solvent uniformly. Following that, alumina sol as a binder is added to the mixture. Then the mixture is sucked and dehydrated using a vacuum pump, and further dried up and sintered. The alumina short fibers form a main portion of the skeleton. Hereupon, if the lengths of the alumina short fibers are smaller, there may be such a tendency that the time required for sucking the mixture extremely increases while the amount of deformation of the preform after the sintering process may increases. On the contrary, if the lengths of the alumina short fibers are longer, each of the components in the mixture is non-uniformly dispersed so that larger non-reinforced regions may be formed in the compounded portion.
The present invention, which has been developed to solve the above-mentioned problems, has an object to provide a method of manufacturing a preform for compounding use, which can restrain deformation of the preform and formation of larger non-reinforced regions in a compounded portion.
According to the present invention, which has been developed to solve the above-mentioned problems and to achieve the above-mentioned object, there is provided a method of manufacturing a preform for compounding use which is to be impregnated with a molten metal to be compounded with a matrix material. The method includes the step of mixing short fibers, ceramic particles and a binder material together to make a mixture. The average of the lengths of the short fibers is 100 to 200 xcexcm. The volumetric percentage (i.e. volumetric rate) of the short fibers is 1 to 7%. The content of the binder material in the mixture is 0.3 to 5.0 mass %. In addition, the method includes the steps of forming the mixture so as to have a predetermined shape, and sintering the mixture at a temperature of 1000 to 1150xc2x0 C. to form the preform.
According to the above-mentioned method, the average of the lengths of the short fibers is set to a smaller value in order to restrain formation of a larger non-reinforced region in a compounded portion. In order to restrain deformation of the preform due to the shorter fibers during the sintering process, the amount of the binder is balanced with the sintering temperature. In consequence, the strength of the preform may be well maintained while the deformation of the preform may be prevented.
In the above-mentioned method, it is preferable that whiskers are added to the mixture in the step of mixing. If so, the whiskers as the skeleton of the preform improve the strength of the preform. Further, the ceramic particles may be better dispersed.
In the above-mentioned method, it is also preferable that the ceramic particles include particles having a first average diameter and particles having a second average diameter, which is smaller than the first average diameter. In that case, the particles having the second average diameter may be effectively interposed between the short fibers and the particles having the first average diameter so that the degree of sintering of the preform may be improved as a whole.
In the above-mentioned method, it is also preferable that the average of diameters (thickness) of the short fibers is 3 to 5 xcexcm. If so, the strength of the preform may be better maintained while the deformation of the preform may be more effectively prevented.
In the above-mentioned method, it is also preferable that the short fibers are composed of alumina. In that case, the strength of the preform may be more effectively improved.
In the above-mentioned method, it is also preferable that the binder material is composed of alumina sol. In that case, the strength of the preform may be much more effectively improved.
In the above-mentioned method, it is also preferable that the particles having the first average diameter are composed of silicon carbide while the particles having the second average diameter are composed of titanium oxide. If so, the wear resistance and strength of the preform may be more effectively improved.
In the above-mentioned method, it is also preferable that the volumetric percentage of the whiskers in the mixture is 1 to 4%. In that case, the strength of the preform may be better improved. Further, the ceramic particles may be much better dispersed.